1. Field of the Invention
The present invention relates to a hypoid gear structure, and more particularly, relates to a hypoid gear structure having an excellent abnormal-sound prevention property.
2. Description of the Related Art
A technique for using a hypoid gear in a motor-driven power steering device is known. In such a technique, the hypoid gear is disposed as a decelerating mechanism between a rotation axis of an electric motor for providing an auxiliary force for steering and an output axis of a steering system. The rotation axis of the electric motor and the output axis of the steering system are coupled with each other by the hypoid gear structure which functions as a decelerating mechanism.
One problem of the above conventional motor-driven power steering device is that it is difficult to appropriately set a backlash produced at the engaging portion of gears in the hypoid gear structure.
For example, Japanese Laid-Open Publication No. 7-232651 discloses that such a backlash produced at the engaging portion of gears can be appropriately controlled by adjusting the position at which a hypoid ring gear is attached in the vertical direction.
In the conventional hypoid gear structure described in the above-mentioned publication, the engagement between the hypoid ring gear and a hypoid pinion gear is adjusted so that an appropriate backlash is obtained at a correct meshed position between the hypoid ring gear and the hypoid pinion gear. This allows for smooth engagement therebetween. However, if the hypoid gear structure receives a vibration and the like from the side of the tires (from the road surface), an abnormal sound such as a tooth striking sound may be generated due to a backlash even if the backlash is within an appropriate range.